That is correct - since the Nikonos lenses are water contact they don't have the same AOV as a land lens behind a dome port.

CheersJames

(Full disclosure: I work for PiratePro and did most of the design engineering on the housings and lens adapters.)

I always thought the Nikonos 15mm lenses were rectilinear lenses with very low pincushion or barrel distortion underwater. If that's the case, then the ray of light from the subject (through water) to the front nodal point has to be parallel to the ray of light from the rear nodal point to the image on the focal plane. In an air-contact rectilinear lens, those two rays also have to be parallel. Doesn't this mean that the Nikonos 15mm lenses have the same AOV in water as air-contact rectilinear 15mm lenses in air?

If you have a low distortion air-contact 15mm lens behind a dome port, and that dome port is centered around the front nodal point of the lens, you should approximate the angel of view of the Nikonos 15mm. If the dome port isn't centered on the front nodal point, or if you use a 15mm lens behind a flat port, then the AOV will be different. The angle of view will also be different if you use a high distortion lens like the Tokina 10-17 (the Nikonos will have more AOV corner-to corner, but less AOV top-to-bottom). I'm not disparaging the Tokina 10-17, that's a great lens, but it has the distortion of any fisheye lens, and it really complicates the AOV equations.

The marketing of this lens as a 15 mm by Nikon was an advertising strategy as much as it was truth. If the Nikonos 15 mm, 20 mm or 28 mm lenses are used out of the water they will retain the AOV of the same above water lenses. In the case of the 15 mm 110 degrees, you just won't be able to find a point of sharp focus with the lens above water. Used under water the AOV is reduced to around 94 degrees (as with a 20 mm above water) and sharp focus can be obtained. In contrast the after market 18 mm rectilinear made for the Nikonos RS is the Nikon lens mount and guts of a Nikkor 18 mm land lens mounted behind a large dome port. This lens will focus as well above water as below and retains the same AOV both above and below water.

David,

Since the Nikonos lenses were designed for the 35 mm format (36 x 24 MM) and they are being mounted on a M4:3 sensor (18 x 13.5 MM or smaller) it appears to me that the 15 mm Nikonos lens AOV would be reduced from 94 degrees to 47 degrees and that the rest of the Nikonos lens lines AOV would also be reduced by the same X2 crop factor. Is this in fact the case? Also since these lenses are all manual focus lenses do they allow the in focus green dot to come on when focus is obtained? also will this housing have a port mounting system as well so that the M4:3 lenses can be used like the old SubEye film system that could use both housed Nikon lenses and the Nikonos RS lenses with an adapter?

Since the Nikonos lenses were designed for the 35 mm format (36 x 24 MM) and they are being mounted on a M4:3 sensor (18 x 13.5 MM or smaller) it appears to me that the 15 mm Nikonos lens AOV would be reduced from 94 degrees to 47 degrees and that the rest of the Nikonos lens lines AOV would also be reduced by the same X2 crop factor. Is this in fact the case?

The AOV of the 15mm lens WILL be reduced, from 94 degrees to somewhere around 58 degrees. This ratio is a little different from the crop factor because the AOV of a rectilinear lens changes with twice the arctangent of the sensor size divided by twice the focal length; putting the arctangent function in that equation makes it extremely nonlinear, so halving the sensor size doesn't halve the AOV.

We are also making adapters that will hold the lens 4mm closer to the sensor, which will increase the AOV by various amounts. They will work like the opposite of an extension tube (extension tube decrease the AOV and icnrease the magnification, the reducing adapter will increase th AOV and decrease the magnification). This is a rarely used optical trick that only works on short focal length lenses being adapted to a smaller lens mount in a format that uses a smaller sensor.

I haven't tested the 12mm Sea & Sea fisheye lens, but I expect it to have a fairly wide FOV, especially on the reducing adapter. An angle of view of around 130 degrees (equivalent to a 10mm rectilinear lens in air) seems likely, but I don't know the exact distortions imparted by the Sea & Sea fisheye.

Also since these lenses are all manual focus lenses do they allow the in focus green dot to come on when focus is obtained?

I haven't been able to get the EP1 to reliably show the green dot with manual lenses. I've been focusing by looking at the screen to check the focus. I've also checked the focus by using the info mode where a press of the "OK" button magnifies a window of the screen by 10X. If you're interested in the behavior of the EP1 with manual lenses, there are many people using the EP1 with Leica lenses.

also will this housing have a port mounting system as well so that the M4:3 lenses can be used like the old SubEye film system that could use both housed Nikon lenses and the Nikonos RS lenses with an adapter?

No, it won't.

I haven't seen the SubEye system, but I would be fascinated to take apart that adapter. As I understand it, the RS lenses don't use the standard Nikon F-mount mechanical controls for focus and aperture, so an adapter would need some swiss-watch style linkages to transfer motion.

As for ports for other lenses (like the four-thirds 8mm fisheye, the 20mm f/1.7, or the 50mm f/2.0 macro), we're not offering those, at least not in the first run of products. Our goal is to add a new capability to the marketplace: the ability to take digital pictures through Nikonos lenses. We don't have much to add to the products that let you take photos from behind ports. In the future, we might add a product that lets you do both, but that's not the focus right now.

The camera has a Nikon mount that takes Nikon lenses and a bayonet mount system to enclose the lenses with what ever port works for that lens. The RS lenses also mount to the standard Nikon lens mount and have a short extension ring that bayonets to the camera side and accepts the lens o-ring on the lens side sealing the lens to the housing. The lenses all move via a power button that moves the elements of the lens in and out with the same type of motor that drives an auto focus lens. It is to slow to auto focus but works as a power focus and can be used with both land and RS lenses.

In your Q&A section no reference is made to the "crop factor" which will apply using Nikonos lenses on the M 4:3 sensor.

Thanks to your suggestions, the FAQ section has been updated to include:1. The angular field of view, 2. The focal length of a lens with same field of view when used with a full-frame sensor and a dome port, and 3. The focal length of a lens with same field of view when used with a full-frame sensor and a flat port with water outside the flat port.

If anybody has suggestions for better or clearer ways to communicate the lens field of view or 35mm equivalent information, I'd love to hear them.

Also, thank you to everyone who pointed out that the 15mm lens has a 94 degree AOV, instead of the normal AOV of a rectilinear lens with a 15mm focal length.

I've been following this topic with high interest. As many of us, I was a big fan of the Nikonos sytem when I started to take pictures underwater. I think the Nikonos V+ 15 mm was a light and fast camera when taking pictures freediving. For example when taking pictures of dolphins and whales, so I am waiting with high interest what's going on with the Pirate Pro project.

There's something that I always wanted to ask about the Rs lenses. Maybe some of you can answer that!
I remember the 18 mm made by Rene Aumann. As some of you pointed, it was a Nikon land lens behind a dome. I never had one, but I was told that this 18 mm was usable in both, Rs body and Nikon F land bodies. In the other hand the RS lenses were not usable on Nikon land bodies. Does anybody know why? I've been comparing the rear bayonet of RS and Nikon lenses and are almost identical, so I never understood why the RS lenses did not work on a Nikon land bodies.

In the other hand the RS lenses were not usable on Nikon land bodies. Does anybody know why? I've been comparing the rear bayonet of RS and Nikon lenses and are almost identical, so I never understood why the RS lenses did not work on a Nikon land bodies.

The backs of Nikon F-mount and Nikonos-RS lenses are similar, but not quite identical. This site describes the Nikon F-mount features better than I ever could. Using the terminology of that site, my 50mm Nikonos-RS lens is missing feature 2 (the groove that tells the camera the focal length of the lens) and feature 4 (the tab that tells the camera the maximum aperture of the lens).

Even though the bayonet mount will let me mount the 50mm Nikonos-RS lens to my Nikon D90, the lack of the groove and tab means that my camera won't recognize the lens, and won't engage the focus or aperture controls. I can still take pictures with the camera in M mode, but the lens is locked at minimum aperture and the only way to change the focus is to point the lens up (focus moves to infinity) or down (focus moves closer).